In a large mixing bowl, mix the flour, sugar, baking powder, and salt. Then mix in the milk, eggs, butter, and vanilla extract. Mix well.
Use butter and GENEROUSLY coat your skillet. If you do not have a skillet, use a small pan.
Pour the batter into the prepared pan.
In a small mixing bowl, mix the brown sugar, butter, and ground cinnamon. Mix well.
Add the topping on top, and then use a spoon and swirl the brown-sugar mix-in into the cake.
Place the pan into the air fryer at 320 degrees F for 12-15 minutes. (air fryer setting)
In a small bowl, make the icing, mix the powdered sugar and milk, and then drizzle over the cake.
Wait a couple of minutes until the icing sets.
Slice.
Plate, serve, and enjoy!